Fuel cell stack

ABSTRACT

An opening is formed in an accommodating case of a fuel cell stack. Flat cables are led out of the accommodating case through the opening. The flat cables pass through a grommet covering the opening. The grommet is positioned by a seal plate (positioning member) attached to the accommodating case.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/723,780, filed Oct. 3, 2017 which is based upon and claimsthe benefit of priority from Japanese Patent Applications No.2016-197976 filed on Oct. 6, 2016, No. 2016-197982 filed on Oct. 6,2016, No. 2016-201986 filed on Oct. 13, 2016, No. 2016-201998 filed onOct. 13, 2016, and No. 2016-245506 filed on Dec. 19, 2016, the contentsall of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a fuel cell stack including a cablepassing through an opening of an accommodating case.

Description of the Related Art

For example, a solid polymer electrolyte fuel cell includes a powergeneration cell (unit fuel cell). An anode is provided on one surface ofan electrolyte membrane, and a cathode is provided on the other surfaceof the electrolyte membrane to form a membrane electrode assembly (MEA).The electrolyte membrane is a polymer ion exchange membrane. Themembrane electrode assembly is sandwiched between separators to form thepower generation cell.

In the fuel cell of this type, in use, in order to obtain a desiredelectrical energy in power generation, a predetermined number of (e.g.,several tens to several hundreds of) power generation cells are stackedtogether to form a fuel cell stack. In this type of the fuel cell stack,it is necessary to detect whether or not each of the power generationcells has the desired power generation performance. For this purpose,generally, a cell voltage detection terminal provided on the separatoris connected to a voltage detection device (cell voltage monitor) todetect the cell voltage of each of the power generation cells duringpower generation (e.g., see Japanese Laid-Open Patent Publication No.2000-223141).

SUMMARY OF THE INVENTION

According to safety regulations of the fuel cell stack, it is requiredto provide a gas barrier structure for preventing leakage of hydrogen tothe outside of the fuel cell stack. For compliance with suchregulations, in the fuel cell stack, the gas barrier structure isrealized by accommodating a cell stack body formed by stacking aplurality of power generation cells in an accommodating case.

Further, in order to connect the cell voltage detection terminalprovided on the separator, to the voltage detection device, whilemaintaining the gas barrier structure using the accommodating case, itmay be considered to provide a grommet at an opening of theaccommodating case, insert cables through a hole formed in the grommet,and then seal the hole. In this case, the cables need to be led out ofthe accommodating case through the grommet provided at the opening ofthe accommodating case, while achieving a desired seal performance forthe accommodating case.

However, at the time of assembling the grommet to the accommodatingcase, depending on the assembling method, part of the grommet may bedropped into the opening, and the grommet may be assembled obliquely. Insuch a case, there is a risk that the desired sealing performance maynot be achieved. It may be considered to provide a step for positioningthe grommet in the accommodating case. However, if the grommet rides onthe step and is assembled obliquely, there is also a risk that thedesired sealing performance may not be obtained.

For example, in some cases, the fuel cell stack is made up of severalhundreds of power generation cells. In a technique of inserting severalhundreds of cables one by one through respective grommet holes andsealing the grommet holes individually, since the size of the grommetbecome large as a whole, it is not possible to provide the spacesufficient for the grommet having the large size. In an attempt toaddress the problem, it may be considered to use flat cables (flatharness) each having a plurality of lead wires (unit wires) that arearranged in parallel, to thereby gather the cables into one location forsize reduction. In this case, it is desired that the flat cables are ledout of the accommodating case through the grommet provided at theopening of the accommodating case, while maintaining the desired sealingperformance of the accommodating case.

An object of the present invention is to solve at least one of the abovedescribed problems.

That is, an object of the present invention is to provide a fuel cellstack which makes it possible to easily achieve a desired sealingperformance with respect to a location where a cable passes through anaccommodating case.

Further, another object of the present invention is to provide a fuelcell stack which makes it possible to reduce the size of a grommet byusing a flat cable, and realize a seal structure without any gas leakagefrom an accommodating case.

In order to achieve the above object, according to an aspect of thepresent invention, a fuel cell stack including a cell stack body, and anaccommodating case configured to accommodate the cell stack body isprovided. The cell stack body includes a plurality of power generationcells stacked. Each of the power generation cells is formed by stackinga membrane electrode assembly and a separator. The membrane electrodeassembly includes a pair of electrodes and an electrolyte membraneinterposed between the electrodes. A cable connected to the cell stackbody in the accommodating case passes through an opening formed in theaccommodating case, and the cable is led out of the accommodating case.The cable passes through a grommet covering the opening, and the grommetis positioned with respect to the opening by a positioning memberattached to the accommodating case.

In the fuel cell stack of the present invention, the grommet ispositioned with respect to the accommodating case by the positioningmember attached to the accommodating case. In the structure, since thegrommet is positioned by the positioning member, positional displacementof the grommet relative to the opening is suppressed greatly. Therefore,the grommet is not damaged by friction against the accommodating case,and it is possible to prevent the grommet from being dropped into theopening (in the case where a step is provided on the accommodating case,it is also possible to prevent the grommet from riding on the step).Therefore, it is possible to achieve a desired sealing performanceeasily. Further, at the time of assembling, since it is possible toeasily position the grommet with respect to the opening, shortening oftime required for assembling operation can be expected as well.

Further, according to another aspect of the present invention, a fuelcell stack including a cell stack body, and an accommodating caseconfigured to accommodate the cell stack body is provided. The cellstack body includes a plurality of power generation cells stacked. Eachof the power generation cells is formed by stacking a membrane electrodeassembly and a separator. The membrane electrode assembly includes apair of electrodes and an electrolyte membrane interposed between theelectrodes. A cell voltage detection terminal is provided on theseparator, a flat cable is connected to the cell voltage detectionterminal, the flat cable passes through an opening formed in theaccommodating case, and the flat cable is led out of the accommodatingcase. A grommet having a slit is provided at the opening, and the slitpasses through the grommet in the thickness direction. The flat cable isinserted through the slit, and sealed hermetically by a potting portionprovided adjacent to the grommet. The grommet includes a cable insertionportion having the slit, and a flange annularly arranged around thecable insertion portion and facing the accommodating case. A pluralityof seals are annularly arranged in lines along the flange, between theflange and the accommodating case.

In the fuel cell stack, the outer peripheral portion of the flat cablepassing through the opening of the accommodating case is sealedhermetically by the potting portion. Therefore, it is possible to reducethe size of a grommet used for adopting the flat cable, and realize aseal structure without any gas leakage from the accommodating case.Since the seals in the plurality of lines are provided between theflange of the grommet and the accommodating case, it is possible tosuppress improper assembling due to inclination of the seal, and achievethe desired sealing performance.

Further, according to still another aspect of the present invention, afuel cell stack including a cell stack body, and an accommodating caseconfigured to accommodate the cell stack body is provided. The cellstack body includes a plurality of power generation cells stacked. Eachof the power generation cells is formed by stacking a membrane electrodeassembly and a separator. The membrane electrode assembly includes apair of electrodes and an electrolyte membrane interposed between theelectrodes. A cell voltage detection terminal is provided on theseparator, a flat cable is connected to the cell voltage detectionterminal, the flat cable passes through an opening formed in theaccommodating case, and the flat cable is led out of the accommodatingcase. A grommet having a slit is provided at the opening, and the slitpasses through the grommet in the thickness direction. The flat cable isinserted through the slit, and sealed hermetically by a potting portionprovided adjacent to the grommet. The grommet includes a cable insertionportion having the slit, and a plurality of ridge-shaped seals which areannularly arranged in lines around the outside of the cable insertionportion and arranged side-by-side in a direction in which the openingpasses through the accommodating case.

In the fuel cell stack, since the grommet includes the plurality ofseals arranged in the plurality of lines and arranged side-by-side inthe direction in which the opening passes through the accommodatingcase, it is possible to suppress improper assembling due to inclinationof the seals, and achieve the desired sealing performance.

Further, according to still another aspect of the present invention, afuel cell stack of including a cell stack body, and an accommodatingcase configured to accommodate the cell stack body is provided. The cellstack body includes a plurality of power generation cells stacked. Eachof the power generation cells is formed by stacking a membrane electrodeassembly and a separator. The membrane electrode assembly includes apair of electrodes and an electrolyte membrane interposed between theelectrodes. A cell voltage detection terminal is provided on theseparator, a flat cable is connected to the cell voltage detectionterminal, the flat cable passes through an opening formed in theaccommodating case, and the flat cable is led out of the accommodatingcase. A grommet having a slit is provided at the opening, and the slitpasses through the grommet in the thickness direction. The flat cable isinserted through the slit, and sealed hermetically by a potting portionprovided adjacent to the grommet. The potting portion includes a firstpotting layer adjacent to the grommet and a second potting layeradjacent to the first potting layer on an opposite side from thegrommet.

In the fuel cell stack of the present invention, the outer peripheralportion of the flat cable passing through the opening of theaccommodating case is sealed by the potting portion including the firstpotting layer and the second potting layer. Therefore, it is possible toreduce the size of the grommet used for adopting a flat cable, andrealize a seal structure without any gas leakage from the accommodatingcase.

Further, according to still another aspect of the present invention, afuel cell stack including a cell stack body, and an accommodating caseconfigured to accommodate the cell stack body is provided. The cellstack body includes a plurality of power generation cells stacked. Eachof the power generation cells is formed by stacking a membrane electrodeassembly and a separator. The membrane electrode assembly includes apair of electrodes and an electrolyte membrane interposed between theelectrodes. A cell voltage detection terminal is provided on theseparator, a flat cable is connected to the cell voltage detectionterminal, the flat cable passes through an opening formed in theaccommodating case, and the flat cable is led out of the accommodatingcase. A grommet made of EPDM is provided at the opening, the grommethaving a slit passing through the grommet in the thickness direction.The flat cable is inserted through the slit, and sealed hermetically bya potting portion made of silicone, the potting portion being providedadjacent to the grommet through an intermediate layer. The intermediatelayer is provided between the grommet and the potting portion, and madeof a material which does not inhibit hardening of a silicone pottingmaterial in the liquid state.

When the silicone potting material in the liquid state contacts EPDM,the silicone potting material is not easily hardened. In the fuel cellstack, the intermediate layer which does not inhibit hardening of aliquid silicone potting material is provided between the grommet made ofEPDM and the potting portion. Accordingly, it is possible to harden thesilicone potting material in the liquid state reliably.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a fuel cell stack according to afirst embodiment of the present invention;

FIG. 2 is a view schematically showing the fuel cell stack;

FIG. 3 is a perspective view showing a seal structure of flat cables;

FIG. 4 is a cross sectional view showing the seal structure;

FIG. 5 is a perspective view showing a grommet of the seal structure;

FIG. 6A is a cross sectional view showing the grommet taken along a lineVIA-VIA in FIG. 5;

FIG. 6B is a cross sectional view showing the grommet according to amodified embodiment;

FIG. 7 is an enlarged cross sectional view showing first seal ridges;

FIG. 8 is a cross sectional view showing the first seal ridges andcomponents around the first seal ridges that are assembled together;

FIG. 9 is a cross sectional view showing second seal ridges and aflange, taken along a line IX-IX in FIG. 5;

FIG. 10 is a cross sectional view showing the second seal ridges and theflange that are assembled together;

FIG. 11A is a perspective view showing a seal plate of the sealstructure as viewed from an upper surface of the seal plate;

FIG. 11B is a perspective view showing the seal plate of the sealstructure as viewed from a lower surface of the seal plate;

FIG. 12 is an enlarged cross sectional view showing first seal ridgesaccording to a modified example;

FIG. 13 is a cross sectional view showing second seal ridges and aflange according to the modified example;

FIG. 14 is a cross sectional view showing a seal structure of a fuelcell stack according to a second embodiment;

FIG. 15 is a cross sectional view showing a seal structure of a fuelcell stack according to a third embodiment;

FIG. 16 is a cross sectional view showing main part of a grommet, apotting portion, and an intermediate portion;

FIG. 17 is a perspective view showing a sheet of an intermediate layer;and

FIG. 18 is a cross sectional view showing a seal structure of a fuelcell stack according to a fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of a fuel cell stack according to thepresent invention will be described with reference to the accompanyingdrawings.

A fuel cell stack 10 according to a first embodiment of the presentinvention shown in FIG. 1 is mounted, e.g., in a fuel cell electricvehicle (not shown). The fuel cell stack 10 includes a cell stack body13 formed by stacking a plurality of power generation cells 12 (unitfuel cells) and an accommodating case 14 accommodating the cell stackbody 13. In FIG. 1, a plurality of power generation cells 12 are stackedtogether in a horizontal direction indicated by an arrow B such thatelectrode surfaces of the power generation cells 12 are orientedupright. It should be noted that the plurality of power generation cells12 may be stacked together in the gravity direction indicated by anarrow C.

As shown in FIG. 2, each of the power generation cells 12 includes amembrane electrode assembly 16, and a first separator 18 and a secondseparator 20 sandwiching the membrane electrode assembly 16. Forexample, the first separator 18 and the second separator 20 are metalplates such as steel plates, stainless steel plates, aluminum plates,plated steel sheets, or metal plates having anti-corrosive surfaces bysurface treatment.

Each of the first separator 18 and the second separator 20 has arectangular surface, and is formed by corrugating a metal thin plate bypress forming to have a corrugated shape in cross section and a wavyshape on the surface. Instead of the metal separators, for example,carbon separators may be used as the first separator 18 and the secondseparator 20.

The membrane electrode assembly 16 includes an anode 24 and a cathode26, and a solid polymer electrolyte membrane 22 interposed between theanode 24 and the cathode 26. The solid polymer electrolyte membrane 22is formed by impregnating a hydrocarbon based thin film or a thinmembrane of perfluorosulfonic acid with water, for example.

Though not shown in detail, each of the anode 24 and the cathode 26 hasa gas diffusion layer such as a carbon paper, and an electrode catalystlayer of platinum alloy supported on porous carbon particles. The carbonparticles are deposited uniformly on the surface of the gas diffusionlayer. For example, the electrode catalyst layer of the anode 24 and theelectrode catalyst layer of the cathode 26 are formed on both surfacesof the solid polymer electrolyte membrane 22, respectively.

The cell stack body 13 has an oxygen-containing gas supply passage (notshown) for supplying an oxygen-containing gas and an oxygen-containinggas discharge passage (not shown) for discharging the oxygen-containinggas. The oxygen-containing gas supply passage and the oxygen-containinggas discharge passage extend through the plurality of power generationcells 12 in the stacking direction indicated by the arrow B.

Further, the cell stack body 13 has a fuel gas supply passage (notshown) for supplying a fuel gas such as a hydrogen-containing gas and afuel gas discharge passage (not shown) for discharging the fuel gas. Thefuel gas supply passage and the fuel gas discharge passage extendthrough the plurality of power generation cells 12 in the stackingdirection indicated by the arrow B.

Further, the cell stack body 13 has coolant supply passages 32 a forsupplying a coolant and coolant discharge passages 32 b for dischargingthe coolant (see FIG. 1). The coolant supply passages 32 a and thecoolant discharge passages 32 b extend through the plurality of powergeneration cells 12 in the stacking direction indicated by the arrow B.

In FIG. 2, the first separator 18 has a fuel gas flow field 28 on itssurface 18 a facing the membrane electrode assembly 16. The fuel gasflow field 28 extends, for example, in the direction indicated by thearrow A. The fuel gas flow field 28 is connected to the fuel gas supplypassage and the fuel gas discharge passage described above.

On the other hand, the second separator 20 has an oxygen-containing gasflow field 30 on its surface 20 a facing the membrane electrode assembly16. The oxygen-containing gas flow field 30 extends, for example, in thedirection indicated by the arrow A. The oxygen-containing gas flow field30 is connected to the oxygen-containing gas supply passage and theoxygen-containing gas discharge passage described above.

A coolant flow field 34 is formed between a surface 18 b of the firstseparator 18 of one of the adjacent power generation cells 12 and asurface 20 b of the second separator 20 of the other of the adjacentpower generation cells 12. The coolant flow field 34 is connected to thecoolant supply passages 32 a and the coolant discharge passages 32 b(see FIG. 1). The coolant flow field 34 is formed by stacking the backsurface of the fuel gas flow field 28 and the back surface of theoxygen-containing gas flow field 30.

The embodiment of the present invention adopts a cooling structure wherecells each formed by sandwiching one MEA 16 between two separators arestacked together, and the coolant flows between the adjacent cells. Itshould be noted that so called skip cooling structure where coolantflows at intervals of every predetermined number of cells may beadopted. In this case, each of the cells includes three or moreseparators and two or more MEAs.

At one end of the power generation cells 12 in the stacking direction, afirst terminal plate 36 a is provided. A first insulating plate 38 a isprovided outside the first terminal plate 36 a. A first end plate 40 ais provided outside the first insulating plate 38 a. At the other end ofthe power generation cells 12 in the stacking direction, a secondterminal plate 36 b is provided. A second insulating plate 38 b isprovided outside the second terminal plate 36 b, and a second end plate40 b is provided outside the second insulating plate 38 b.

Though not shown, an oxygen-containing gas supply manifold member, anoxygen-containing gas discharge manifold member, a fuel gas supplymanifold member, and a fuel gas discharge manifold member are attachedto the first end plate 40 a. The oxygen-containing gas supply manifoldmember is connected to the oxygen-containing gas supply passage. Theoxygen-containing gas discharge manifold member is connected to theoxygen-containing gas discharge passage. The fuel gas supply manifoldmember is connected to the fuel gas supply passage. The fuel gasdischarge manifold member is connected to the fuel gas dischargepassage.

As shown in FIG. 1, a coolant supply manifold member 42 a and a coolantdischarge manifold member 42 b are attached to the second end plate 40b. The coolant supply manifold member 42 a is connected to a pair ofcoolant supply passages 32 a. The coolant discharge manifold member 42 bis connected to a pair of coolant discharge passages 32 b.

Two sides (surfaces) of the accommodating case 14 at both ends in thevehicle width direction indicated by the arrow B are the first end plate40 a and the second end plate 40 b. Two sides (surfaces) of theaccommodating case 14 at both ends in the vehicle length directionindicated by the arrow A are a front side panel 44 a and a rear sidepanel 44 b each having a laterally elongated plate shape. Two sides(surfaces) of the accommodating case 14 at both ends in the vehicleheight direction indicated by the arrow C are an upper side panel 46 aand a lower side panel 46 b. The upper side panel 46 a and the lowerside panel 46 b each have a laterally elongated plate shape.

The front side panel 44 a and the rear side panel 44 b are fixed to thefirst end plate 40 a and the second end plate 40 b using screws 48 in anair tight manner and a liquid tight manner. Further, the upper sidepanel 46 a and the lower side panel 46 b are fixed to the first endplate 40 a, the second end plate 40 b, the front side panel 44 a, andthe rear side panel 44 b using screws 48 in an air tight manner and aliquid tight manner. In this manner, the accommodating case 14 is formedby assembling the first end plate 40 a, the second end plate 40 b, thefront side panel 44 a, the rear side panel 44 b, the upper side panel 46a, and the lower side panel 46 b together.

The above described accommodating case 14 functions as a gas isolationstructure (gas barrier) for preventing leakage of reactant gases such asa hydrogen gas to the outside of the accommodating case 14.

As shown in FIG. 2, a cell voltage detection terminal 50 is provided oneach of the power generation cells 12. The cell voltage detectionterminal 50 protrudes downward from a lower side of the above describedfirst separator 18 (or the second separator 20). The cell voltagedetection terminal 50 may be provided at any position of the abovedescribed first separator 18 (or the second separator 20). In the casewhere the skip cooling structure having the three separators is adopted,the cell voltage detection terminal 50 is provided, for example, on aseparator at an intermediate position.

A flat cable (flat harness) 54 is connected to the cell voltagedetection terminal 50 through a connector 52. The structure of the cellvoltage detection terminal 50 is not limited specially as along as thecell voltage detection terminal 50 can be electrically connected to theflat cable 54. In the fuel cell stack 10 according to the embodiment ofthe present invention, a plurality of flat cables 54 are provided. Theconnector 52 is fixed to the inner surface (specifically, inner surfaceof the lower side panel 46 b) of the accommodating case 14. The flatcable 54 is a band-shaped cable formed by combining a plurality of leadwires arranged in parallel together, and having substantially flatsurfaces on both sides in the thickness direction.

The plurality of flat cables 54 are stacked together in the thicknessdirection, inside the accommodating case 14. As shown in FIGS. 2 and 3,the plurality of flat cables 54 extend to the outside of theaccommodating case 14 through an opening 14 a formed in theaccommodating case 14 (specifically, the lower side panel 46 b). Theopening 14 a has a non-circular shape. In FIG. 3, the opening 14 a has asubstantially rectangular shape rounded at each corner. The opening 14 amay have a different non-circular shape (e.g., elliptical shape, etc.).The plurality of flat cables 54 are connected to a cell voltagedetection device (not shown), outside the accommodating case 14. Forexample, the cell voltage detection device is fixed to an outer surface46 b 1 of the accommodating case 14. The cell voltage detection devicedetects the cell voltage (electromotive force) of each of the powergeneration cells 12 during power generation.

As shown in FIGS. 3 and 4, a seal structure 56 is provided at theopening 14 a of the accommodating case 14 (lower side panel 46 b). Theseal structure 56 seals the outer peripheral portions of the pluralityof flat cables 54 by a potting portion 62. As shown in FIG. 4, the sealstructure 56 includes a grommet 58 which covers the opening 14 a, a sealplate 60 (positioning member) provided at the opening 14 a, and thepotting portion 62 provided at the seal plate 60.

The grommet 58 is provided on an outer surface 46 b 1 (lower surface) ofthe lower side panel 46 b in a manner to cover the opening 14 a. Thegrommet 58 tightly contacts the lower side panel 46 b at a seal portionthereof (second seal ridges 84) in an air tight manner and liquid tightmanner. A grommet placement recess 14 b is provided on the outer surface46 b 1 of the lower side panel 46 b through a step 14 c, around theopening 14 a. The grommet placement recess 14 b is recessed toward aninner surface 46 b 2 of the lower side panel 46 b. The grommet 58 isplaced in the grommet placement recess 14 b. A plurality of slits 64 areformed in the grommet 58. The slits 64 pass through the grommet 58 inthe thickness direction of the grommet 58.

As shown in FIG. 5, the plurality of slits 64 are spaced from oneanother in a direction perpendicular to the thickness direction of thegrommet 58. The grommet 58 has a shape elongated in one directionperpendicular to the thickness direction. The plurality of slits 64extend in parallel to each other in the longitudinal direction of thegrommet 58.

In FIG. 6A, preferably, the interval L between the plurality of slits 64(interval between the centers of the adjacent slits 64 in the slit widthdirection) is, e.g., in a range of 1 to 5 mm, depending on the viscosityof the potting material (resin material) used for forming the pottingportion 62.

A narrow part 68 is provided at one end of the slit 64 in a direction(one end closer to the opening 14 a) in which the slit 64 passes throughthe grommet 58. The narrow part 68 forms a constricted portion which isthinner than the other part of the slit 64. In FIG. 4, the narrow part68 contacts both surfaces of the flat cable 54.

As shown in FIG. 6A, a wide part 70 is provided at the other end of theslit 64 in the direction in which the slit 64 passes through the grommet58. The slit width of the wide part 70 is larger than the slit width ofthe narrow part 68. A taper part 72 is provided between the narrow part68 and the wide part 70. The slit width of the taper part 72 isincreased toward the wide part 70. Part of the slit 64 other than thenarrow part 68 (taper part 72 and wide part 70) does not necessarilyhave to contact both surfaces of the flat cable 54. For example, in thecase where the wide part 70 does not contact both surfaces of the flatcable 54 (in the case where the slit width of the wide part 70 is largerthan the thickness of the flat cable 54), the wide part 70 allows theflat cable 54 to move in the slit width direction. Further, in thiscase, the grommet 58 can be formed easily.

A lip part 66 may be provided in each slit 64 as in the case of agrommet 58 according to a modified embodiment shown in FIG. 6B. The twolip parts 66 are provided on respective mutually-facing slit surfaces,which are the inner surfaces of the slit 64, so as to protrude towardeach other. For example, two pairs of lip parts 66 are provided at aninterval in the thickness direction of the grommet 58 (in the directionin which the slit 64 passes through the grommet 58).

The lip parts 66 form constricted portions which are narrower than theother part of the slit 64. In the case where the flat cable 54 isinserted into the slit 64 having the lip parts 66, the lip parts 66contact both surfaces of the flat cable 54. In this case, part of theslit 64 other than the lip parts 66 need not contact both surfaces ofthe flat cable 54.

As shown in FIGS. 4 and 5, the grommet 58 includes a mating protrusion74 (cable insertion portion) which protrudes toward the opening 14 a(seal plate 60), a flange 76 provided outside the mating protrusion 74and annularly arranged around the mating protrusion 74, and anintermediate portion 78 between the mating protrusion 74 and the flange76. A plurality of slits 64 described above are formed in the matingprotrusion 74.

As shown in FIG. 5, the mating protrusion 74 extends in the longitudinaldirection of the grommet 58, and first seal ridges 80 protruding outwardare provided on the outer circumferential surface (lateralcircumferential surface) of the mating protrusion 74. The first sealridges 80 extend (are annularly arranged) along the entire circumferenceof the outer circumferential surface of the mating protrusion 74. Thefirst seal ridges 80 are arranged in a plurality of lines (two seallines in the illustrated embodiment) at intervals in the direction inwhich the mating protrusion 74 protrudes (in the direction in which theslits 64 pass through the grommet 58). It should be noted that only onefirst seal ridge 80 (i.e., only one seal line) may be provided.Alternatively, the three or more first seal ridges 80 (i.e., three ormore seal lines) may be provided. The first seal ridges 80 arranged inthe plurality of lines may have different heights (heights in which thefirst seal ridges 80 protrude from the outer circumferential surface ofthe mating protrusion 74).

In FIG. 4, the plurality of first seal ridges 80 protrude from the outercircumferential surface 74 b of the mating protrusion 74, toward theinner circumferential surface of a mating recess 88 b of the seal plate60 described later. That is, the plurality of first seal ridges 80 areformed integrally with the mating protrusion 74. The plurality of firstseal ridges 80 tightly contact the inner circumferential surface of themating recess 88 b along the entire periphery. In the structure, anair-tight and liquid-tight seal portion is formed between the outercircumferential surface 74 b of the mating protrusion 74 and the innercircumferential surface of the mating recess 88 b.

The tip (protruding end) of the first seal ridge 80 may be rounded so asto bulge in a direction in which the first seal ridge 80 protrudes.Hereafter, for the purpose of making a distinction between the one firstseal ridge 80 on one of two lines and the other first seal ridge 80 onthe other of the two lines, the first seal ridge 80 on the upper side(closer to the potting portion 62) will be referred to as the “upperseal 80 a”, and the first seal ridge 80 on the lower side “(farther fromthe potting portion 62)” will be referred to as the “lower seal 80 b”.

As shown in FIG. 4, the intermediate portion 78 is extended outward froman end opposite from the opening 14 a of the mating protrusion 74, andthen curved toward the opening 14 a. In the structure, a ring shapedgroove 82 is formed around the mating protrusion 74, between the matingprotrusion 74 and the intermediate portion 78.

The flange 76 extends outward from the outer circumferential edge of theintermediate portion 78. The plurality of second seal ridges 84 (theplurality of seal lines) are annularly arranged in the plurality oflines along the flange 76, between the flange 76 and the accommodatingcase 14. In the first embodiment, the two second seal ridges 84 in twolines are provided. It should be noted that only one second seal ridge84 (i.e., only one seal line) may be provided. Alternatively, three ormore second seal ridges 84 (i.e., three or more seal lines) may beprovided. The tip (protruding end) of the second seal ridge 84 may berounded so as to bulge in the direction in which the second seal ridge84 protrudes. Hereinafter, in the first embodiment, for the purpose ofmaking a distinction between the one second seal ridge 84 on one of twolines and the other second seal ridge 84 on the other of the two lines,the second seal ridge 84 on the outer side will be referred to as the“outer seal 84 a”, and the second seal ridge 84 on the inner side willbe referred to as the “inner seal 84 b”.

The second seal ridges 84 in the plurality of lines protrude from asurface 76 a of the flange 76 facing the accommodating case 14 (lowerside panel 46 b) toward the outer surface of the accommodating case 14(outer surface 46 b 1 of the lower side panel 46 b). That is, theplurality of second seal ridges 84 are formed integrally with the flange76.

The second seal ridges 84 tightly contact the outer circumferentialsurface (outer surface 46 b 1) of the accommodating case 14 along theentire circumference. In the structure, an air-tight and liquid-tightseal portion is formed between the flange 76 and the outer surface 46 b1 of the accommodating case 14.

As shown in FIG. 7, in a non-compressed state, the plurality of firstseal ridges 80 (the plurality of seal lines) have different crosssections (sizes). Therefore, in the non-compression state, the pluralityof first seal ridges 80 have different cross sectional areas. In thisregard, when the first seal ridges 80 are “in the non-compressed state”,no external force is applied to the first seal ridges 80, and no elasticdeformation from the initial state occurs. That is, the “non-compressedstate” is a state where the grommet 58 is not assembled to theaccommodating case 14 and the seal plate 60, i.e., the state before thegrommet 58 is assembled to the accommodating case 14 and the seal plate60, or the state where the grommet 58 is detached from the accommodatingcase 14 and the seal plate 60. Further, the “cross sectional area” ofthe first seal ridge 80 is an area of the first seal ridge 80 in crosssection (lateral cross section) perpendicular to the direction in whichthe first seal ridge 80 extends.

In the first embodiment, when the first seal ridges 80 are in thenon-compressed state, the protruding height H1 b in lateral crosssection of the lower seal 80 b (the seal provided on a side farther fromthe potting portion 62, of the adjacent first seal ridges 80 among thefirst seal ridges 80 arranged in the plurality of lines) is higher thanthe protruding height H1 a in lateral cross section of the upper seal 80a (the seal provided on a side closer to the potting portion 62, of theadjacent first seal ridges 80 among the first seal ridges 80 arranged inthe plurality of lines), over the entire first seal ridges 80 in thedirection in which the first seal ridges 80 extend (at any positionalong the entire circumference of the first seal ridges 80). In thisregard, the “protruding height” of the upper seal 80 a and the lowerseal 80 b is the protruding height from a surface (the outercircumferential surface 74 b of the mating protrusion 74 in the firstembodiment) on which the upper seal 80 a and the lower seal 80 b areprovided.

The ratio of the protruding height H1 b of the lower seal 80 b to theprotruding height H1 a of the upper seal 80 a is, e.g., in a range of110% to 140%.

Further, in the first embodiment, when the first seal ridges 80 are inthe non-compressed state, the width W1 b of the lower seal 80 b islarger than the width W1 a of the upper seal 80 a, over the entire firstseal ridges 80 in which the first seal ridges 80 extends (at anyposition along the entire circumference of the first seal ridges 80).The “width” of the upper seal 80 a and the “width” of the lower seal 80b herein mean the dimensions in a direction perpendicular to theprotruding height direction at the base of the upper seal 80 a and atthe base of the lower seal 80 b, respectively (the dimension in thedirection in which the opening 14 a passes through the accommodatingcase 14).

The ratio of the width W1 b of the lower seal 80 b to the width W1 a ofthe upper seal 80 a is, e.g., in a range of 120% to 240%.

As shown in FIG. 4, in the state where the grommet 58 is attached to theaccommodating case 14 (lower side panel 46 b) and the seal plate 60, thegrommet 58 is pressed against the accommodating case 14 through abracket 86 (see FIG. 4) described later. Therefore, each of the firstseal ridges 80 in the plurality of lines are compressed in the heightdirection, and placed in an elastically compressed state. As a result,as shown in FIG. 8, the first seal ridges 80 in the plurality of lineshave the same protruding height from the outer circumferential surface74 b of the mating protrusion 74. Therefore, the first seal ridges 80 inthe plurality of lines have different compression ratios. In the firstembodiment, the compression ratio of the larger lower seal 80 b ishigher than the compression ratio of the smaller upper seal 80 a. InFIG. 8, the cross sectional area of the lower seal 80 b is larger thanthe cross sectional area of the upper seal 80 a. In FIG. 8, initialshapes of the first seal ridges 80 in the plurality of lines are denotedby imaginary lines.

As shown in FIG. 9, in a non-compressed state, the second seal ridges 84in the plurality of lines have different cross sectional shapes (sizes).Therefore, in the non-compressed state, the second seal ridges 84 in theplurality of lines have different cross sectional areas. In this regard,when the second seal ridges 84 are “in the non-compressed state”, noexternal force is applied to the second seal ridges 84, and no elasticdeformation from the initial shape occurs. That is, the “non-compressedstate” is a state where the grommet 58 is not assembled to theaccommodating case 14, i.e., the state before the grommet 58 isassembled to the accommodating case 14, or the state where the grommet58 is detached from the accommodating case 14. The “cross sectionalarea” of the second seal ridge 84 is an area of the second seal ridge 84in cross section (lateral cross section) perpendicular to the directionin which the second seal ridge 84 extends.

In the first embodiment, when the second seal ridge 84 is in thenon-compressed state, the height H2 a in lateral cross section of theouter seal 84 a (the seal provided on the outer side, of the adjacentsecond seal ridges 84 among the second seal ridges 84 arranged in theplurality of lines) is higher than the height H2 b in lateral crosssection of the inner seal 84 b (the seal provided on the inner side, ofthe adjacent second seal ridges 84 among the second seal ridges 84 inthe plurality of lines), over the entire second seal ridges 84 in thedirection in which the second seal ridges 84 extend (at any positionalong the entire circumference of the second seal ridges 84). In thisregard, the “height” of the outer seal 84 a and the inner seal 84 b isthe protruding height from the flange 76 (surface 76 a).

The ratio of the height H2 a of the outer seal 84 a to the height H2 bof the inner seal 84 b is, e.g., in a range of 110% to 140%.

Further, in the first embodiment, when the second seal ridges 84 are inthe non-compressed state, the width W2 a of the outer seal 84 a islarger than the width W2 b of the inner seal 84 b, over the entiresecond seal ridges 84 in the direction in which the second seal ridges84 extend (at any position along the entire circumference of the secondseal ridges 84). The “width” of the outer seal 84 a and the “width” ofthe inner seal 84 b herein mean the dimensions in a directionperpendicular to the height direction at the base of the outer seal 84 aand at the base of the inner seal 84 b, respectively (the dimension inthe direction in which the outer seal 84 a and the inner seal 84 b arespaced away from each other).

The ratio of the width W2 a of the outer seal 84 a to the width W2 b ofthe inner seal 84 b is, e.g., in a range of 120% to 240%.

As shown in FIG. 10, in the state where the grommet 58 is attached tothe accommodating case 14 (lower side panel 46 b), the grommet 58 ispressed against the accommodating case 14 by the bracket 86 (see FIG. 4)described later. Therefore, each of the second seal ridges 84 in theplurality of lines are compressed in the height direction, and placed inan elastically compressed state. As a result, the second seal ridges 84in the plurality of lines have the same protruding height from theflange 76 (surface 76 a). Therefore, the second seal ridges 84 in theplurality of lines have different compression ratios. In the firstembodiment, the compression ratio of the larger outer seal 84 a ishigher than the compression ratio of the smaller inner seal 84 b. InFIG. 10, the cross sectional area of the outer seal 84 a is larger thanthe cross sectional area of the inner seal 84 b. In FIG. 10, initialshapes of the second seal ridges 84 in the plurality of lines aredenoted by imaginary lines.

For example, the grommet 58 is made of seal material, cushion material,or packing material, having elasticity, such as an EPDM rubber (ethylenepropylene diene monomer), an NBR (nitrile butadiene rubber), a fluororubber, a silicone rubber, a fluorosilicone rubber, a butyl rubber, anatural rubber, a styrene rubber, a chloroprene rubber, or an acrylicrubber.

As shown in FIG. 4, the grommet 58 is fixed to the accommodating case 14(lower side panel 46 b) by the bracket 86. The bracket 86 is a platemember having a hole 86 a passing through the plate member in thethickness direction. The bracket 86 is firmly fixed to the accommodatingcase 14 by fixing members (not shown) such as screws. The bracket 86 ismade of material (e.g., hard resin, metal, etc.) which is harder thanthe material of the grommet 58.

A part (the mating protrusion 74 and the intermediate portion 78described above) of the grommet 58 is inserted into the hole 86 a, andthe part of the grommet 58 inserted into the hole 86 a protrudes fromthe hole 86 a of the bracket 86. The bracket 86 abuts against the flange76 of the grommet 58, and presses the flange 76 against the outersurface 46 b 1 of the accommodating case 14.

The seal plate 60 positions the grommet 58 in the accommodating case 14in a manner that the grommet 58 is positioned at a suitable positionrelative to the opening 14 a. The seal plate 60 is attached to theopening 14 a.

As shown in FIGS. 4, 11A, and 11B, the seal plate 60 includes a tubularcircumferential wall 88, an outer plate 90 protruding outward from thetubular circumferential wall 88, and an engagement wall 92 protrudingfrom the outer plate 90 to face the tubular circumferential wall 88 at adistance from the tubular circumferential wall 88. As in the case of theabove described grommet 58, the seal plate 60 has a shape elongated inone direction. As shown in FIGS. 11A and 11B, the tubularcircumferential wall 88 is elongated in the longitudinal direction ofthe seal plate 60.

As shown in FIG. 4, a plurality of flat cables 54 are inserted throughthe inside of the tubular circumferential wall 88, and led out of theaccommodating case 14.

An accommodating recess 88 a is provided at one end of the tubularcircumferential wall 88 (inside of the accommodating case 14). Thepotting portion 62 is accommodated (filled) in the accommodating recess88 a. One end of the accommodating recess 88 a is tapered. A matingrecess 88 b is provided at the other end of the tubular circumferentialwall 88 (outside of the accommodating case 14). The mating recess 88 bis opened toward the grommet 58. The mating protrusion 74 is fitted intothe mating recess 88 b. Therefore, the tubular circumferential wall 88functions as a holder portion for holding the grommet 58 inside a claw92 a described later. The tubular circumferential wall 88 protrudesbeyond an insertion portion 91 described later, toward the grommet 58.

The accommodating recess 88 a and the mating recess 88 b are connectedto each other inside the tubular circumferential wall 88, and form athrough hole passing through the seal plate 60 in the thicknessdirection. A protrusion wall 88 c protruding inward is formed on theinner surface of the tubular circumferential wall 88. The protrusionwall 88 c forms a boundary wall between the accommodating recess 88 aand the mating recess 88 b.

The inner circumferential portion of the mating recess 88 b contacts(tightly contacts) the outer circumferential portion (the abovedescribed first seal ridges 80) of the mating protrusion 74 over theentire circumference. In the structure, a gas-tight and liquid-tightseal portion is formed between the inner circumferential portion of themating recess 88 b and the outer circumferential portion of the matingprotrusion 74.

The outer plate 90 protrudes outward from the one end of the tubularcircumferential wall 88. The outer edge portion of the outer plate 90faces the inner surface 46 b 2 (inner surface around the opening 14 a)of the lower side panel 46 b. The engagement wall 92 is elasticallydeformable inward (toward the tubular circumferential wall 88), andinserted into the opening 14 a.

A plurality of engagement walls 92 are provided along the outercircumference of the seal plate 60. As shown in FIG. 11B, the engagementwalls 92 include a pair of engagement walls 92L extending in parallel toeach other in the longitudinal direction of the seal plate 60, and apair of engagement walls 92S extending in parallel to each other in thelateral direction of the seal plate 60. The pair of engagement walls 92Sare shorter than the pair of engagement walls 92L.

As shown in FIG. 4, the seal plate 60 is attached to the opening 14 afrom the side opposite from the grommet 58 (from the inside of theaccommodating case 14 in FIG. 4). The seal plate 60 includes aninsertion portion 91 which extends along the shape (non-circular shape)of the opening 14 a and is inserted into the opening 14 a. Theengagement walls 92 form at least part of the insertion portion 91. Theouter surface 91 a of the insertion portion 91 contacts the innercircumferential surface 14 as of the opening 14 a, or faces the innercircumferential surface 14 as through a small gap as shown in FIG. 4.

The engagement wall 92 includes the claw (engagement portion) 92 a. Theclaw 92 a is engaged with the outer surface (the outer surface of aninner circumferential edge 14 d around the opening 14 a) of the lowerside panel 46 b. The claw 92 a is engaged with the inner circumferentialedge 14 d inside the second seal ridges 84. When the grommet 58 isattached to the opening 14 a, the engagement wall 92 is elasticallydeformed inward. Thus, the claw 92 a moves beyond the innercircumferential surface 14 as of the opening 14 a, and the claw 92 a isengaged with the inner circumferential edge 14 d.

The claw 92 a and the second seal ridges 84 contact a surface of theaccommodating case 14 (inner circumferential edge 14 d) on one side. Thelower side panel 46 b (edge around the opening 14 a) is held between theouter plate 90 and the claw 92 a. Thus, the seal plate 60 is fixed tothe lower side panel 46 b (opening 14 a).

The seal plate 60 is made of material which is harder than that of thegrommet 58. For example, the seal plate 60 is made of hard resin.Examples of the material of the seal plate 60 include PPS (polyphenylenesulfide) or PEEK (polyetheretherketone) based engineering plastics orsuper engineering plastics, etc.

As shown in FIG. 4, the potting portion 62 is accommodated (filled) inthe accommodating recess 88 a adjacent to the mating protrusion 74 ofthe grommet 58. The plurality of flat cables 54 are sealed by thepotting portion 62. The potting portion 62 tightly contacts the outerperipheral portion of each of the flat cables 54. Therefore, spacesbetween the adjacent flat cables 54 are also filled with the pottingportion 62. Further, the potting portion 62 tightly contacts a topsurface 74 a (protruding end surface) of the mating protrusion 74 of thegrommet 58, and tightly contacts the inner circumferential surface ofthe accommodating recess 88 a.

The potting portion 62 includes a first potting layer 62 a adjacent tothe grommet 58, and a second potting layer 62 b adjacent to the firstpotting layer 62 a on the opposite side from the grommet 58. That is,the potting portion 62 includes two potting layers stacked in thedirection in which the opening 14 a passes through the accommodatingcase 14. In the first embodiment, the thickness of the second pottinglayer 62 b is larger than the thickness of the first potting layer 62 a.

The viscosity of the resin material of the first potting layer 62 a(viscosity of the first potting material in the liquid state (beforehardening) which is poured into the accommodating recess 88 a forforming the first potting layer 62 a) is higher than the viscosity ofthe resin material of the second potting layer 62 b (viscosity of thesecond potting material in the liquid state (before hardening) which ispoured into the accommodating recess 88 a for forming the second pottinglayer 62 b). The hardness of the first potting layer 62 a formed byhardening the first potting material is higher than the hardness of thesecond potting layer 62 b formed by hardening the second pottingmaterial.

Examples of the resin material (potting material) of the first pottinglayer 62 a and the second potting layer 62 b include silicone basedpotting material, urethane based potting material, epoxy based pottingmaterial, etc. The potting material preferably should be two-componenttype potting material which is hardened by chemical reaction inducedwhen a base agent and a hardening agent are mixed together.

In the step of forming the potting portion 62, the seal plate 60 isfixed to the opening 14 a (accommodating case 14), the mating protrusion74 of the grommet 58 is fitted into the mating recess 88 b of the sealplate 60, and the flat cables 54 are inserted into the slits 64,respectively. In this state, the potting material is poured into theaccommodating recess 88 a.

Next, operation of the fuel cell stack 10 having the above structurewill be described below.

In FIG. 2, an oxygen-containing gas is supplied to the oxygen-containinggas flow field 30 of the power generation cell 12 through theoxygen-containing gas supply passage (not shown). A fuel gas such as ahydrogen-containing gas is supplied to the fuel gas flow field 28 of thepower generation cell 12 through the fuel gas supply passage (notshown). Further, a coolant such as pure water, ethylene glycol or oil issupplied to the coolant supply passages 32 a of the power generationcell 12 (see FIG. 1).

Therefore, the oxygen-containing gas moves along the oxygen-containinggas flow field 30, and the oxygen-containing gas is supplied to thecathode 26 of the membrane electrode assembly 16. In the meanwhile, thefuel gas moves along the fuel gas flow field 28, and the fuel gas issupplied to the anode 24 of the membrane electrode assembly 16. Thus, inthe membrane electrode assembly 16, the oxygen-containing gas suppliedto the cathode 26 and the fuel gas supplied to the anode 24 are consumedin the electrochemical reactions at catalyst layers of the cathode 26and the anode 24 for generating electricity.

Then, the oxygen-containing gas supplied to and consumed at the cathode26 of the membrane electrode assembly 16 is discharged through theoxygen-containing gas discharge passage (not shown). In the meanwhile,the fuel gas supplied to and consumed at the anode 24 of the membraneelectrode assembly 16 is discharged through the fuel gas dischargepassage (not shown).

Further, the coolant supplied into the coolant flow field 34 movesthrough the coolant flow field 34 to cool the membrane electrodeassembly 16, and thereafter, the coolant is discharged through thecoolant discharge passages 32 b (see FIG. 1).

During operation (power generation) of the fuel cell stack 10, as shownin FIG. 2, each of the power generation cells 12 is connected to a cellvoltage detection device (not shown) through the flat cable 54 connectedto the cell voltage detection terminal 50. Therefore, the voltage(electromotive force) of each power generation cell 12 is measured bythe cell voltage detection device.

In the fuel cell stack 10 according to the first embodiment, as shown inFIG. 4, the grommet 58 is positioned with respect to the opening 14 a bythe seal plate 60 (positioning member) attached to the accommodatingcase 14. In the structure, the grommet 58 is positioned by the sealplate 60, and thus, positional displacement of the grommet 58 relativeto the opening 14 a is suppressed greatly. Therefore, the grommet 58 isnot damaged by friction against the accommodating case 14, and it ispossible to prevent the grommet 58 from being dropped into the opening14 a (In the case where a step 14 c is provided on the accommodatingcase 14, it is also possible to prevent the grommet 58 from riding onthe step 14 c). Therefore, since the grommet 58 is prevented from beingassembled in a state where the grommet 58 is inclined, it is possible toachieve the desired sealing performance easily. Further, at the time ofassembling, since the grommet 58 can be easily positioned relative tothe opening 14 a, shortening of time required for performing assemblingoperation can be expected as well.

In the first embodiment, the seal plate 60 is attached to the opening 14a. Since the seal plate 60 is positioned at the opening 14 a, it ispossible to suppress positional displacement of the grommet 58 to agreater extent.

In the first embodiment, the opening 14 a has a non-circular shape, andthe seal plate 60 includes the insertion portion 91. The insertionportion 91 extends along the shape of the opening 14 a, and is insertedinto the opening 14 a. In the structure, the grommet 58 is positionedrelative to the opening 14 a in the rotation direction (because rotationof the grommet 58 relative to the opening 14 a is restricted) as well asin the plane direction. Therefore, it is possible to suppress thepositional displacement of the grommet 58 to a greater extent.

In the first embodiment, the seal plate 60 includes the claw 92 a(engagement portion) which is engaged with the inner circumferentialedge 14 d of the opening 14 a, and the tubular circumferential wall 88(holder portion) holding the grommet 58 inside the claw 92 a. Therefore,since the seal plate 60 is held by the opening 14 a, and the grommet 58is held by the tubular circumferential wall 88, it is possible tosuppress the positional displacement of the grommet 58 suitably to agreater extent.

In the first embodiment, the claw 92 a and the second seal ridge 84contact the surface of the accommodating case 14 on one side, and theclaw 92 a is engaged with the inner circumferential edge 14 d inside thesecond seal ridges 84. Therefore, it is possible to fix the seal plate60 at the opening 14 a suitably, without inhibiting the sealingperformance of the second seal ridges 84.

In the first embodiment, the grommet 58 includes the mating protrusion74 protruding toward the seal plate 60. The seal plate 60 includes themating recess 88 b opened toward the grommet 58 and into which themating protrusion 74 is fitted. In the structure, by fitting the matingrecess 88 b and the mating protrusion 74 together, since the grommet 58is held accurately, it is possible to suppress the positionaldisplacement of the grommet 58 more suitably.

In the first embodiment, the flat cables 54 are inserted through themating protrusion 74. In the structure, the mating protrusion 74 has afunction of being held by the seal plate 60, and also has a function ofallowing the flat cables 54 to be inserted through the mating protrusion74. Therefore, it is possible to simplify the structure of the grommet58.

In the first embodiment, the seal plate 60 is attached to the opening 14a, from the side opposite to the grommet 58. Therefore, it is possibleto assemble the seal plate 60 and the grommet 58 to the opening 14 a ofthe accommodating case 14 easily.

In the first embodiment, the bracket 86 pressing the outercircumferential portion of the grommet 58 is fixed to the accommodatingcase 14. Therefore, it is possible to suitably fix the grommet 58 to theaccommodating case 14, and improve the sealing performance between theaccommodating case 14 and the grommet 58.

In the fuel cell stack 10, as shown in FIG. 4, the outer peripheralportions of the flat cables 54 passing through the opening 14 a of theaccommodating case 14 are sealed hermetically by the potting portion 62including the first potting layer 62 a and the second potting layer 62b. Therefore, it is possible to reduce the size of the grommet 58 usedfor adopting the flat cables 54, and realize a seal structure 56 withoutany gas leakage (leakage of reactant gases such as a hydrogen-containinggas) from the accommodating case 14.

In FIG. 4, as shown by dashed arrows, a reactant gas such as a hydrogengas may enter the grommet 58 side from the accommodating case 14 througha space between the accommodating case 14 (lower side panel 46 b) andthe seal plate 60.

In this regard, in the first embodiment, as shown in FIG. 4, the firstseal ridges 80 are provided on the outer circumferential portion of themating protrusion 74 of the grommet 58, and the first seal ridges 80tightly contact the inner circumferential portion of the mating recess88 b of the seal plate 60. Therefore, it is possible to prevent thereactant gas such as a hydrogen gas from passing through a gap betweenthe mating protrusion 74 and the mating recess 88 b and being leakedfrom the accommodating case 14 to the outside through the slits 64.

In particular, in the first embodiment, since the grommet 58 includesthe first seal ridges 80 arranged in the plurality of lines, it ispossible to suppress improper assembling due to inclination of thegrommet 58, and achieve the desired sealing performance. That is, unlikethe first embodiment, in the case where the seal lip between the matingprotrusion 74 and the mating recess 88 b has a single-seal-linestructure (in the case where the first seal ridge 80 only in one line isprovided), if the seal has a height sufficient to assemble the seal at atolerance height that allows the durability to be guaranteed, thegrommet 58 may be assembled obliquely, depending on the assemblingmethod. In this case, it is likely that the seal lip is not compressed,or some part of the seal lip is not compressed sufficiently, andconsequently, the desired sealing performance may not be obtained.

In contrast, in the first embodiment, as described above, the grommet 58includes the first seal ridges 80 arranged in the plurality of lines.That is, a multiple-seal-line structure is provided between the matingprotrusion 74 and the mating recess 88 b. Therefore, even if the sealhas a height sufficient to assemble the seal at a tolerance height whichallows the durability to be guaranteed, it is possible to suppress asituation where the grommet 58 is assembled to the accommodating case 14obliquely. Therefore, improper assembling of the grommet 58 issuppressed, and it is possible to reliably achieve the desired sealingperformance.

Further, in the first embodiment, in the non-compressed state, the firstseal ridges 80 in the plurality of lines have different cross sectionalshapes. Therefore, even if there is any change in the seal tighteningmargin (compression condition) due to the tolerance of component partsor variation in assembling, it becomes possible to improve therobustness of the air-tight seal (hydrogen seal). That is, the sealcompression ratio varies significantly due to the tolerance of componentparts or variation in assembling. Under the circumstances, if the sealcompression ratio becomes too high due to the tolerance of componentparts or variation in assembling, cracking of the seal may occurundesirably. Conversely, if the seal compression ratio becomes too low,permanent set-in fatigue may occur in the seal, and in the worst case,leakage of hydrogen may occur. Further, in the case where the sealheight is not sufficient, it is difficult to assemble the seal withinthe tolerance height which guarantees the durability.

In contrast, in the first embodiment, as described above, in thenon-compressed state, the first seal ridges 80 in the plurality of lineshave different cross sectional shapes. Therefore, even if the sealcompression ratio varies due to the tolerance of component parts orvariation in assembling, it is possible to achieve the desired sealingperformance in at least one of the first seal ridges 80. That is, evenif the seal compression ratio becomes too high in the larger first sealridge 80 (the lower seal 80 b having a larger height and width in thefirst embodiment), and cracking occurs, since the seal compression ratiois not so high (within a suitable range) in the smaller first seal ridge80 (the upper seal 80 a), no cracking occurs, and thus it is possible tomaintain the desired sealing performance suitably. Further, even if theseal compression ratio in the smaller first seal ridge 80 (upper seal 80a) becomes excessively small, since the larger first seal ridge 80(lower seal 80 b) has a suitable seal compression ratio, the desiredsealing performance can be maintained suitably.

Further, in the first embodiment, in the non-compressed state, the firstseal ridges 80 (upper seal 80 a and lower seal 80 b) which are adjacentto each other among the first seal ridges 80 in the plurality of linesare dimensioned such that the seal provided farther from the pottingportion 62 (lower seal 80 b) is larger than the seal (upper seal 80 a)provided closer to the potting portion 62 in respect of the protrudingheight in lateral cross section and the width in the directionperpendicular to the direction of the protruding height. Therefore, itis possible to more suitably prevent the situation where the grommet 58is assembled to the accommodating case 14 obliquely. Accordingly, it ispossible to suppress improper assembling of the grommet 58, and reliablyachieve the desired sealing performance.

Further, in the first embodiment, the second seal ridges 84 are providedon the flange 76 of the grommet 58, and the second seal ridges 84tightly contact the outer surface of the accommodating case 14. In thestructure, it is possible to prevent the reactant gas such as thehydrogen gas from passing through a gap between the flange 76 of thegrommet 58 and the outer surface of the accommodating case 14, and beingleaked from the accommodating case 14 to the outside.

In particular, in the first embodiment, since the second seal ridges 84arranged in the plurality of lines are provided between the flange 76 ofthe grommet 58 and the accommodating case 14, it is possible to suppressimproper assembling due to inclination of the grommet 58, and achievethe desired sealing performance. That is, unlike the first embedment, inthe case where the seal lip has a single-seal-line structure (in thecase where the second seal ridge 84 only in one line is provided), ifthe seal has a height sufficient to assemble the seal at a toleranceheight that allows the durability to be guaranteed, the grommet 58 maybe assembled obliquely, depending on the assembling method. In thiscase, it is likely that the seal lip is not compressed, or some part ofthe seal lip is not compressed sufficiently, and consequently, thedesired sealing performance may not be obtained.

In contrast, in the first embodiment, as described above, the secondseal ridges 84 are arranged in the plurality of lines between the flange76 of the grommet 58 and the accommodating case 14. That is, amultiple-seal-line structure is provided. Therefore, even if the sealhas a height sufficient to assemble the seal at a tolerance height whichguarantees the durability, it is possible to suppress the situationwhere the grommet 58 is assembled to the accommodating case 14obliquely. Therefore, it is possible to suppress improper assembling ofthe grommet 58, and achieve the desired sealing performance reliably.

Further, in the first embodiment, in the non-compressed state, thesecond seal ridges 84 in the plurality of lines have different crosssectional shapes. Therefore, even if there is any change in the sealtightening margin (compression condition) due to the tolerance ofcomponent parts or variation in assembling, it becomes possible toimprove the robustness of the air-tight seal (hydrogen seal). That is,the seal compression ratio varies significantly due to the tolerance ofcomponent parts or variation in assembling. Under the circumstances, ifthe seal compression ratio becomes too high due to the tolerance ofcomponent parts or variation in assembling, cracking of the seal mayoccur undesirably. Conversely, if the seal compression ratio becomes toolow, permanent set-in fatigue may occur in the seal, and in the worstcase, leakage of hydrogen may occur. Further, in the case where the sealheight is not sufficient, it is difficult to assemble the seal withinthe tolerance height which guarantees the durability.

In contrast, in the first embodiment, as described above, in thenon-compressed state, the second seal ridges 84 in the plurality oflines have different cross sectional shapes. Therefore, even if the sealcompression ratio varies due to the tolerance of component parts orvariation in assembling, it is possible to achieve the desired sealingperformance in at least one of the second seal ridges 84. That is, evenif the seal compression ratio becomes too high in the larger second sealridge 84 (the outer seal 84 a having a larger height and width in thefirst embodiment), and cracking occurs, since the seal compression ratiois not so high (within a suitable range) in the smaller second sealridge 84 (the inner seal 84 b), no cracking occurs, and thus it ispossible to maintain the desired sealing performance suitably. Further,even if the seal compression ratio in the smaller second seal ridge 84(inner seal 84 b) becomes excessively small, since the larger secondseal ridge 84 (outer seal 84 a) has a suitable seal compression ratio,the desired sealing performance can be maintained suitably.

Further, in the first embodiment, in the non-compressed state, thesecond seal ridges 84 (outer seal 84 a and inner seal 84 b) which areadjacent to each other among the second seal ridges 84 in the pluralityof lines are dimensioned such that the seal provided on the outside(outer seal 84 a) is larger than the seal on the inner side (inner seal84 b) in respect of the protruding height in lateral cross section fromthe flange 76 and the width in the direction perpendicular to theprotruding height. Therefore, it is possible more suitably to preventthe situation where the grommet 58 is assembled to the accommodatingcase 14 obliquely. Accordingly, it is possible to suppress improperassembling of the grommet 58, and it is possible to achieve the desiredsealing performance.

As shown in FIG. 4, the outer peripheral portion of the flat cable 54passing through the opening 14 a of the accommodating case 14 is sealedhermetically by the potting portion 62. In the structure, it is possibleto reduce the size of the grommet 58 used for adopting of the flat cable54, and achieve the seal structure 56 without any gas leakage (leakageof a reactant gas such as a hydrogen-containing gas) from theaccommodating case 14.

Further, in the first embodiment, the seal plate 60 is provided at theopening 14 a. The seal plate 60 tightly contacts the grommet 58, and hasthe accommodating recess 88 a. Further, the potting portion 62 isaccommodated in the accommodating recess 88 a. In the structure, by theseal plate 60 having the accommodating recess 88 a, it is possible toeasily provide an area sufficient for forming a potting layer around theflat cable 54 passing through the opening 14 a. Accordingly, the outerperipheral portion of the flat cable 54 can be sealed more suitably.

Further, in the first embodiment, as shown in FIG. 4, the flat cables 54are inserted into the plurality of slits 64 arranged in parallel atintervals, respectively. In the structure, the flat cables 54 are heldat intervals by the plurality of slits 64. Therefore, the space betweenthe adjacent flat cables 54 among the plurality of flat cables 54 aresealed by the potting portion 62 as well. Accordingly, the desiredsealing performance is achieved.

Further, in the first embodiment, the viscosity of the resin material ofthe first potting layer 62 a is higher than the viscosity of the resinmaterial of the second potting layer 62 b. Therefore, at the time offorming the potting portion 62, since the viscosity of the pottingmaterial (resin material of the first potting layer 62 a) initiallyfilled is relatively high, it is possible to prevent the pottingmaterial from flowing to the outside through the slits 64. In the stepof forming the potting portion 62, the seal plate 60 is fixed to theopening 14 a (accommodating case 14), the mating protrusion 74 of thegrommet 58 is fitted into the mating recess 88 b of the seal plate 60,and the plurality of flat cables 54 are inserted separately into theplurality of slits 64. In this state, a potting material is poured intothe accommodating recess 88 a.

Further, at the time of forming the potting portion 62, since theviscosity of the potting material (resin material of the second pottinglayer 62 b) filled next is relatively low, the potting material can befilled between the adjacent flat cables 54 among the plurality of flatcables 54 in a short period of time. Further, since the viscosity isrelatively low, the potting material can be filled in the gap reliably,and the desired sealing performance can be obtained. Accordingly, it ispossible to suitably form the potting portion 62 which achieves the highsealing performance.

Additionally, in the first embodiment, as shown in FIGS. 6A and 6B, theslit 64 includes constricted portions (narrow parts 68, lip parts 66).By providing the constricted portions, at the time of forming thepotting portion 62, it is possible to more suitably prevent the pottingmaterial from being leaked to the outside through the slits 64.

The size relationship between the upper seal 80 a and the lower seal 80b is not limited to the above described structure. Therefore, forexample, as shown in FIG. 12, the upper seal 80 a may be larger than thelower seal 80 b. That is, in the first seal ridges 80 in the pluralityof lines shown in FIG. 12, in the non-compressed state, the protrudingheight H1 a of the upper seal 80 a in lateral cross section is higherthan the protruding height H1 b of the lower seal 80 b in lateral crosssection, and the width W1 a of the upper seal 80 a in lateral crosssection is larger than the width W1 b of the lower seal 80 b in lateralcross section.

Alternatively, though the protruding height H1 b of the lower seal 80 bis larger than the protruding height H1 a of the upper seal 80 a, thewidth W1 b of the lower seal 80 b may be smaller than the width W1 a ofthe upper seal 80 a. Alternatively, though the protruding height H1 a ofthe upper seal 80 a is larger than the protruding height H1 b of thelower seal 80 b, the width W1 a of the upper seal 80 a may be smallerthan the width W1 b of the lower seal 80 b.

In the non-compressed state, the seals that are adjacent to each other,among the first seal ridges 80 in the plurality of lines may have thesame height, but have different widths. Alternatively, in thenon-compressed state, the seals that are adjacent to each other, amongthe first seal ridges 80 in the plurality of lines may have differentheights, but have the same width.

The size relationship between the outer seal 84 a and the inner seal 84b is not limited to the above described structure. Therefore, as shownin FIG. 13, the inner seal 84 b may be larger than the outer seal 84 a.That is, in the second seal ridges 84 in the plurality of lines shown inFIG. 13, in the non-compressed state, the height H2 b of the inner seal84 b in lateral cross section is higher than the height H2 a of theouter seal 84 a in lateral cross section, and the width W2 b of theinner seal 84 b in lateral cross section is larger than the width W2 aof the outer seal 84 a in lateral cross section.

Alternatively, though the height H2 a of the outer seal 84 a is largerthan height H2 b of the inner seal 84 b, the width W2 a of the outerseal 84 a may be smaller than the width W2 b of the inner seal 84 b.Alternatively, though the height H2 b of the inner seal 84 b is largerthan the height H2 a of the outer seal 84 a, the width W2 b of the innerseal 84 b may be smaller than the width W2 a of the outer seal 84 a.

The shapes of the outer seal 84 a and the inner seal 84 b may be set ina manner that, though the height H2 a of the outer seal 84 a and theheight H2 b of the inner seal 84 b are the same, the width W2 a of theouter seal 84 a and the width W2 b of the inner seal 84 b are different.Alternatively, the shapes of the outer seal 84 a and the inner seal 84 bmay be determined in a manner that, though the width W2 a of the outerseal 84 a and the width W2 b of the inner seal 84 b are the same, theheight H2 a of the outer seal 84 a and the height H2 b of the inner seal84 b are different.

In the first embodiment, the potting portion 62 have a dual layerstructure including the first potting layer 62 a and the second pottinglayer 62 b, and the first potting layer 62 a and the second pottinglayer 62 b have different physical properties (hardness). Alternatively,as in the case of the fuel cell stack 10 a according to a secondembodiment shown in FIG. 14, a potting portion 62 c having a singlelayer structure may be provided. That is, a seal structure 56 a of thefuel cell stack 10 a includes the potting portion 62 c having a singlelayer structure which does not have a plurality of potting layers ofdifferent hardness.

As shown in FIG. 15, a seal structure 56 b of a fuel cell stack 10 baccording to a third embodiment includes a grommet 58 made of EPDMrubber (ethylene propylene diene monomer) provided at an opening 14 a, aseal plate 60 provided at the opening 14 a, and a potting portion 62made of silicone. The potting portion 62 is provided adjacent to thegrommet 58 (specifically, the mating protrusion 74) through anintermediate layer 94.

A material of each of the first potting layer 62 a and the secondpotting layer 62 b preferably should be a two-component type pottingmaterial, which is hardened by chemical reaction induced when a baseagent and a hardening agent are mixed together.

As shown in FIG. 16, an intermediate layer 94 is provided between thegrommet 58 made of EPDM and the potting portion 62 made of silicone.Specifically, the intermediate layer 94 is provided adjacent to themating protrusion 74 (a top surface 74 a) of the grommet 58. The pottingportion 62 is provided adjacent to the intermediate layer 94 on theopposite side from the mating protrusion 74 of the grommet 58.Therefore, the potting portion 62 does not directly contact the grommet58.

The intermediate layer 94 is made of a material which does not hinderhardening of the silicone potting material in the liquid state. Examplesof the material which does not hinder hardening of the liquid siliconepotting material includes a material which does not includes sulfur,nitrogen compound, or organic metal salt. Silicone, soft urethane, andpolyvinyl chloride are specific examples of the material which does nothinder hardening of the silicone potting material.

The thickness t1 of the intermediate layer 94 is smaller than thethickness t2 of the potting portion 62. In the case where the pottingportion 62 includes a first potting layer 62 a and a second pottinglayer 62 b as in the third embodiment, preferably, the thickness t1 ofthe intermediate layer 94 is smaller than the thickness t3 of the firstpotting layer 62 a. Preferably, the thickness t1 of the intermediatelayer 94 is in a range of 0.3 to 2.0 mm.

For example, the intermediate layer 94 is in the form of a sheet 94 ahaving slit-shaped through holes 94 a 1, and flat cables 54 are insertedinto the through holes 94 a 1. In the case of the third embodiment, asshown in FIG. 16, the sheet 94 a has a plurality of through holes 94 a1, and a plurality of flat cables 54 are inserted into the through holes94 a 1.

As shown in FIG. 17, each of the through holes 94 a 1 extends in alongitudinal direction of the sheet 94 a, and passes through the sheet94 a in the thickness direction. Each of the through holes 94 a 1 hassubstantially the same shape as the shape of the flat cable 54 inlateral cross section so as not to form a gap between the inner surfaceof the through hole 94 a 1 and the flat cable 54 substantially. Itshould be noted that a minute gap which does not allow entry of theliquid potting material may be formed between the flat cable 54 and theinner surface of the through hole 94 a 1.

Further, the sheet 94 a includes a plurality of cut lines 94 a 2. Eachof the cut lines 94 a 2 is connected to one end of each of the pluralityof through holes 94 a 1. Each of the cut lines 94 a 2 extends in thedirection in which the through hole 94 a 1 extends, and reaches themarginal edge of the sheet 94 a.

In the step of forming the potting portion 62 shown in FIG. 15, the sealplate 60 is fixed to the opening 14 a (accommodating case 14), a matingprotrusion 74 of the grommet 58 is fitted into a mating recess 88 b ofthe seal plate 60, and a plurality of flat cables 54 are inserted intothe plurality of slits 64, respectively. In this state, the sheet 94 aof the intermediate layer 94 is provided on the top surface 74 a of themating protrusion 74. In this case, since the plurality of cut lines 94a 2 (see FIG. 17) are formed in the sheet 94 a, each of the flat cables54 can be easily inserted into each of the through holes 94 a 1 througheach of the cut lines 94 a 2. In the structure, the sheet 94 a can beplaced on the top surface 74 a of the mating protrusion 74 easily.

Next, a silicone potting material in the liquid state is poured into theaccommodating recess 88 a. In this case, since the sheet 94 a isprovided on the top surface 74 a of the mating protrusion 74, thepotting material in the liquid state does not contact the matingprotrusion 74 (EPDM). Further, the potting portion 62 is formed byhardening the potting material.

The intermediate layer 94 may comprise a coating portion 94 b made ofacrylic coating, adhesive, etc., instead of the above described sheet 94a. In the step of forming the potting portion 62, the seal plate 60 isfixed to the opening 14 a (accommodating case 14), the mating protrusion74 of the grommet 58 is fitted into the mating recess 88 b of the sealplate 60, and the plurality of flat cables 54 are inserted into theslits 64, respectively. In this state, a liquid coating material such asan acrylic coating, an adhesive, or the like is applied onto the topsurface 74 a of the mating protrusion 74. In this case, in order toprevent the top surface 74 a of the mating protrusion 74 from beingdirectly exposed at the bottom of the accommodating recess 88 a (inorder to cover the entire exposed top surface 74 a at the bottom of theaccommodating recess 88 a), the coating material is applied onto an areaaround the flat cables 54 inserted into the slits 64 and the top surface74 a between the flat cables 54.

After the coating portion 94 b is formed by hardening the liquid coatingmaterial, the silicone potting material in the liquid state is pouredinto the accommodating recess 88 a. In this case, since the coatingportion 94 b is provided on the top surface 74 a of the matingprotrusion 74, the liquid potting material does not contact the matingprotrusion 74 (EPDM). Then, the potting portion 62 is formed byhardening the potting material.

As described above, in the fuel cell stack 10 b according to the thirdembodiment, the intermediate layer 94 which does not inhibit hardeningof the silicone potting material in the liquid state is provided betweenthe grommet 58 made of EPDM and the potting portion 62 made of silicone.Therefore, it is possible to harden the silicone potting material in theliquid state reliably. Specifically, when the silicone potting materialin the liquid state contacts EPDM, the silicone potting material is nothardened easily. Therefore, in the case where the intermediate layer 94is not provided, in the step of forming the potting portion 62, thesilicone potting material in the liquid state directly contacts thegrommet 58 made of EPDM, and consequently the potting material may notbe hardened undesirably.

In contrast, in the third embodiment, the grommet 58 made of EPDM andthe potting portion 62 made of silicone are isolated from each other bythe intermediate layer 94. Therefore, at the time of forming the pottingportion 62, the silicone potting material in the liquid state does notdirectly contact the grommet 58 made of EPDM. Thus, hardening of theliquid silicone potting material is not inhibited. Accordingly, it ispossible to harden the silicone potting material in the liquid statereliably, and it is possible to form the potting portion 62 having thedesired sealing performance suitably.

Further, in the third embodiment, the intermediate layer 94 is made of amaterial which does not include sulfur, nitrogen compound, or organicmetal salt. Therefore, by the intermediate layer 94, it is possible tosuitably prevent inhibition of hardening of the liquid silicone pottingmaterial.

Further, in the third embodiment, as shown in FIG. 16, the intermediatelayer 94 is in the form of the sheet 94 a having the through holes 94 a1, and the flat cables 54 are inserted into the through holes 94 a 1.Therefore, with the simple and economical structure, it is possible toharden the silicone potting material in the liquid state reliably.

As described above, the intermediate layer 94 may comprise a coatingportion 94 b made of an acrylic coating or an adhesive. In this case, bypouring the coating material in the liquid state into the accommodatingrecess 88 a, it is possible to form the intermediate layer 94 withoutany gap between the flat cables 54 and the accommodating recess 88 asimply and reliably.

In the third embodiment, the potting portion 62 has a dual layerstructure including the first potting layer 62 a and the second pottinglayer 62 b, and the first potting layer 62 a and the second pottinglayer 62 b have different physical properties (hardness). As in the caseof a fuel cell stack 10 c according a fourth embodiment shown in FIG.18, a potting portion 62 c having a single layer structure may beprovided. That is, the seal structure 56 c of the fuel cell stack 10 cincludes the potting portion 62 c having a single layer structurewithout having a plurality of potting layers of different hardness.

In the first to fourth embodiments, as the cables connected to the cellvoltage detection terminals 50, the flat cables 54 are used. However,instead of the flat cables 54, cables of other types may be used. Thecables led out of the opening 14 a of the accommodating case 14 may becables other than the cell voltage detection cables.

The present invention is not limited to the above embodiments. Variousmodifications can be made without departing from the gist of the presentinvention.

What is claimed is:
 1. A fuel cell stack comprising: a cell stack bodycomprising a plurality of power generation cells stacked, the powergeneration cells each formed by stacking a membrane electrode assemblyand a separator, the membrane electrode assembly including a pair ofelectrodes and an electrolyte membrane interposed between theelectrodes; and an accommodating case configured to accommodate the cellstack body, wherein a cell voltage detection terminal is provided on theseparator, a flat cable is connected to the cell voltage detectionterminal, the flat cable passes through an opening formed in theaccommodating case, and the flat cable is led out of the accommodatingcase; a grommet made of EPDM is provided at the opening, the grommethaving a slit passing through the grommet in a thickness directionthereof; the flat cable is inserted through the slit, and sealedhermetically by a potting portion made of silicone, the potting portionbeing provided adjacent to the grommet through an intermediate layer;and the intermediate layer is provided between the grommet and thepotting portion, and made of a material which does not inhibit hardeningof a silicone potting material in a liquid state.
 2. The fuel cell stackaccording to claim 1, wherein the intermediate layer is made of amaterial which does not include sulfur, nitrogen compound, or organicmetal salt.
 3. The fuel cell stack according to claim 2, wherein theintermediate layer is in form of a sheet having a through hole intowhich the flat cable is inserted.
 4. The fuel cell stack according toclaim 2, wherein the intermediate layer comprises a coating portion madeof an acrylic coating or an adhesive.